SO-18577504

// http://stackoverflow.com/questions/18577504/y-style-task-execution

static DateTime _startTime;

private static async Task Task1(Task task)
{
    await task.ConfigureAwait(false);
    await Task.Delay(2000).ConfigureAwait(false);
    Console.WriteLine("Task1, lapse: {0}, thread: {1}", (DateTime.Now-_startTime).TotalMilliseconds, Thread.CurrentThread.ManagedThreadId);
}

private static async Task Task2(Task task)
{
    await task.ConfigureAwait(false);
    await Task.Delay(2500).ConfigureAwait(false);
    Console.WriteLine("Task2, lapse: {0}, thread: {1}", (DateTime.Now - _startTime).TotalMilliseconds, Thread.CurrentThread.ManagedThreadId);
}

private static async Task Test3()
{
    _startTime = DateTime.Now;
    var task = Task.Delay(1000);
    var task1 = Task1(task);
    var task2 = Task2(task);
    await Task.WhenAll(task1, task2);
    Console.WriteLine("All finished, lapse: {0}, thread: {1}", (DateTime.Now - _startTime).TotalMilliseconds, Thread.CurrentThread.ManagedThreadId);
}